Method and device for compensating the temperature of circular resonators

ABSTRACT

A method and an arrangement for temperature compensation at circular resonators with dual mode utilization, which includes a material with a low coefficient of thermal expansion and for which the tensile or compressive forces are transferred to the resonator wall and produce elastic deformations there. The resonator wall is deformed in two mutually perpendicular directions in each case by the same absolute amount at one or more places along the axial extent, the deformation forces being introduced into the resonator war over at least one flange. This has the advantage that the peripheral shape of the casing of the circular resonator is deformed so that both orthogonal dual modes experience uniform shortening with simultaneous expansion of the material, as a result of which a high compensation effect is achieved.

The invention is based on a method and an arrangement for thetemperature compensating at circular resonators with dual modeutilization for microwave filters realizable therefrom of the typedefined in the main claim.

Circular resonators, which are used in operating environments in whichthe temperature fluctuates greatly, are equipped with various means forcompensating for the thermal expansion caused by temperaturefluctuations. A frequently employed principle for counteracting thesethermal expansions consists of changing the volume of the circularresonators as a function of the temperature with the help of mechanicalmeans in such a manner, that the transfer properties of the circularresonator are retained. Usually, devices are used for this purpose,which protrude into the interior of the circular resonator (DE 39 35785) and change their volume there as a function of the temperature, sothat the average frequency of the resonator remains constant. A furtherpossibility consists of utilizing the effect of the resonator end faces(EP 0 939 450 A1, WO 87/03745). Compensating elements, which dip more orless into the interior of the resonator, can be adjusted only withdifficulty and, because of the nonlinear field distortion, lead to anonlinear frequency compensation.

In the EP 0 939 450 A1, a circular resonator is closed off by anarrangement at the end face, which consists of two plates with differentcoefficients of thermal expansion, lying rigidly on top of one another.In the WO 87/03745, a curved, thin copper plate protrudes at the endface into the interior of the circular resonator. For certain cases ofapplication, for example, if, because of special quality requirements,so-called TE1 1n modes, with n>1, are used as working modes in circularresonators, the effect of end-side compensation becomes constantly lessbecause of the unfavorable relationships between length and diameter.Especially at high frequencies (Ku, Ka or higher) this technique fails,since the necessary deformation of the end-side diaphragms no longer issufficient.

An arrangement, for which the waveguide is clamped in at least oneframe, the temperature-dependent expansion of which is less than that ofthe waveguide, can compensate for large temperature-dependent volumechanges (DE 43 19 886). Moreover, at least at two mutually oppositeplaces of its wall, the waveguide is connected non-positively with theframe. The frame and waveguide are connected non-positively overspacers, which transfer compression and tensile forces, resulting fromthe different thermal expansions of the frame and the waveguide, ontothe waveguide wall and cause elastic deformations there. The end facesof the waveguide produce the bulk of the elastic deformation. Moreover,deformation forces may be transferred over spacers, disposed between theframe and the casing of the waveguide, also onto the frame andcounteract undesirable buckling of the frame. The disadvantage of thissolution consists therein that, at two opposite side walls, ribs areintegrally molded as spacers to the spacers of the frame, that is, thatthe waveguide of the arrangement must be adapted for the temperaturecompensation, which is associated with additional expense.

In comparison, the inventive method with the characterizingdistinguishing features of claim 1 has the advantage that thecross-sectional shape of the casing of the circular resonator isdeformed so that both orthogonal dual modes, in this case, especiallythe Te1 1n modes, which are mostly used, experience a uniform shorteningwith a simultaneous expansion of the material, as a result of which ahigh compensation effect is achieved. The supporting structure, named inclaim 4, is an arrangement, which ensures a uniform, centrallysymmetrical, radial effect on the casing of the circular resonator. Inpractice, at least two supporting structures are required, whichsurround the circular resonator coaxially. They consist of a materialwith a thermal expansion, which is clearly high than that of thematerial of the circular resonator and are connected at specific sitesover spacers firmly with the flange of the circular resonator. Theforces of the supporting structure, deforming because of the effect oftemperature, are transferred at these places onto the circularresonator. In the regions, in which there are no spacers, the supportingstructures do not contact the circular resonator, so that the flange canbe deformed freely in these regions. The flange carries out a tiltingand pushing movement under the deformation forces of the supportingstructures. The forces, introduced into the flange, are transferred overthe latter to the casing of the circular resonator, so that the latteris deformed so that compensation takes place on both modessimultaneously and uniformly. A further technical translation of themethod consists of letting the forces act directly from outside in twomutually perpendicular directions on the resonator casing. This may beaccomplished, for example, by two clamping elements, which are mutuallyoffset by 90° and accommodate the resonator casing between theirclamping jaws.

According to an advantageous development of the invention, twodisk-shaped supporting structures are provided, which surround thecircular resonator in semicircular fashion and are bolted to the flange.

In a further, advantageous development of the invention, the upperspacers consist of a material, the thermal coefficient of expansion ofwhich is different from that of the lower spacers. By these means, thedeformation of the resonator casing can be improved further.

Further advantages and advantageous developments of the invention may beinferred from the following description and the claims.

An example of the invention is described in greater detail in thefollowing and shown in the drawing, in which

FIG. 1 shows a spatial representation of a cylindrical resonator with asupporting structure mounted at the flange,

FIG. 2 diagrammatically shows the supporting surfaces between the flangeand the supporting structure and

FIG. 3 shows a diagrammatic representation of the deformation on ahighly enlarged scale.

As can be seen from FIG. 1, the cylindrical resonator consists of acylindrical resonator wall 1, which has a flange 2 on both sides. Behindthe front flange 2, there is an upper supporting element 3 and a lowersupporting element 4, which are connected by means of screws 5 with theflange 2. At the connecting sites, between the supporting elements 3, 4and the flange 2, there are spacers 6, of which only one each at thefront and rear flange can be recognized in this representation. Thelower supporting elements 4 differ from the upper supporting elements 3owing to the fact that they have a larger flat region after theirsemicircular recess. This flat region serves for dissipating heat fromthe resonator as well as for fixing the resonator at the adjoiningcomponents.

FIG. 2 shows an upper supporting element 3 and a lower supportingelement 4. The crosshatched regions represent supporting surfaces 7, atwhich the spacers 6 between the flange 2 and the supporting elements 3,4 rest, over which the force is introduced into the cylindricalresonator. The supporting surfaces 7 are disposed so that thedifferential expansion between the cylindrical resonator and thesupporting structure produces the deformation, which is shown on a muchenlarged scale in FIG. 3. The deformation can be improved even more ifspacers 6 with different coefficients of expansions, for example, whenthe upper spacers 6 consist of aluminum and the lower ones of invar, areused at the supporting surfaces 7. The deformation, shown in FIG. 3,shows that the circular resonator, because it is heated to a temperatureT>TO, TO being the initial temperature of the circular resonator, forexample, before it is used, is deformed uniformly in the x and ydirections, as a result of which there is a uniform compensation on bothmodes.

All the distinguishing features, given in the description, the claimsthat follow and in the drawing, may be essential to the inventionindividually as well as in any combination with one another.

LIST OF REFERENCE NUMBERS

-   1 resonator wall-   2 flange-   3 upper supporting element-   4 lower supporting element-   5 screws-   6 spacer-   7 supporting surfaces

1. Method for the temperature compensation at circular resonators withdual mode utilization, which includes a material with a low coefficientof thermal expansion and for which tensile or compressive forces aretransferred to the resonator wall and produce elastic deformationsthere, comprising deforming the resonator wall at one or more placesalong its axial extent in two mutually perpendicular directions by, ineach case, the same absolute amount.
 2. The method of claim 1, whereinthe deformation forces are applied directly to the resonator wall. 3.The method of claim 1, wherein the deformation forces are introducedinto the resonator wall over at least one flange.
 4. Arrangement forcompensating the temperature at circular resonators with dual-modeutilization, which comprises a material with a low coefficient ofthermal expansion and having a flange at their end faces, at least twosupporting structure for each flange, said supporting structurescomprising a material with a coefficient of thermal expansion, higherthan that of the material of the circular resonator, and lie in a planeperpendicular to the axis of the circular resonator and surround thecircular resonator coaxially, which, without touching the resonatorwall, are connected with the flange of the circular resonator overspaces which are distributed uniformly radially.
 5. The arrangement ofclaim 4, wherein two supporting structures are provided which enclosethe circular resonator in each case semicircularly.
 6. The arrangementof claim 4, wherein the spacers have different coefficients ofexpansion.
 7. The arrangement of claim 5, wherein the spacers havedifferent coefficients of expansion.